A Look at DNA Testing

A Look at DNA Testing

copyright 1995 by Robert J. Cadranell from Arabian Visions Mar/Apr 1995 used by permission of RJ Cadranell  

        One topic much discussed in Arabian racing circles (and in all horse racing circles) is how to identify individual animals and make sure that their parentage has been recorded correctly. Arabian racing carries the added twist that surreptitiously introducing blood from another breed, the Thoroughbred, can give an advantage on the track.

        Tina (several people interviewed for this article are identified only by a first name, all of which have been changed) is actively involved with Arabian racing. “There is a widespread feeling that some of the horses on the track might not match their pedigrees,” she says. “People don’t want to get beaten by horses that are part Thoroughbred.”

        Niles grew up with horses, and has owned, raced, and bred Thoroughbreds for more than 20 years. “In the Thoroughbred world, when a record is broken, it’s usually by only a fraction of a second, not several seconds,” he points out. “Occasionally in Thoroughbreds we do turn up what we call a ‘sport,’ and these horses reproduce; St. Simon was one. But anyone who has studied the evolution of the Thoroughbred knows you can’t breed success overnight. And even in inbred Thoroughbred families, there is variance. So, sometimes I’m a little suspicious.”

        None of this makes Diane suspicious. She has owned Arabians for about ten years and is just starting to get involved with the sport of Arabian racing. “Arabian racing is still so new, anyone could turn up the next superhorse,” she contends. “Not all the bloodlines have even been raced yet. There are still far too many unknowns. It’s not like Thoroughbred racing, which has been going on for centuries. I think there’s a lot of talk that’s just gossip and sour grapes.”

        Likely much of it is more rumor than substance. Since the 1920s and earlier Arabian breeders have, from time to time, accused each other of having a Thoroughbred cross in their pedigrees. Most of these stories are probably nonsense. But there have been cases in the last 25 years of Arabian race horses turning in good times on the track and later having their papers canceled because bloodtyping did not qualify them to their purported parents.

        ”The Thoroughbred has been selected for more than 200 years for speed,” Niles says. “The proportion of fast twitch muscle is high. Arabians, on the other hand, have been selected over probably a much longer period of time for endurance: slow twitch muscle. Endurance racing records show the Arabians dominate the sport.”

        How long would a race have to be so the endurance of the Arabian would give it the advantage? Results from the Russian track give an indication. “Empirically it has been shown that only the Thoroughbred is faster than the Arab, but the latter is uncatchable at distances above thirty-five furlongs [4.4 miles].” (1)

        If racing enthusiasts are concerned about keeping things “clean,” would it work to race Arabians over distances long enough that there is no incentive to slip in an Anglo-Arab? “Absolutely not,” Tina answers. “The betting public will not sit through even a three mile race. It’s just too long. We’re struggling now to run on Thoroughbred tracks. The Thoroughbred people would laugh at us.”

        Niles agrees. “The public wants action,” he says. “Younger spectators are already complaining there is too much time between races and not enough excitement.”

        With Arabian racing fixed at the current distances, attention has turned to other means of verifying that everyone is playing by the rules. The problem of correctly identifying horses and their parentage is not unique to Arabian racing. Niles comments, “As a breeder, I don’t want to be dealing with an unknown factor. Thoroughbred racehorses can sell for $500,000 or more, and race for hundreds of thousands — even a million. We don’t want ringers. I have to know what I’m dealing with.”

        DNA testing has been a hot topic recently. Some registration authorities and labs are adding information obtained from DNA testing to the battery of data identifying individual horses. The Arabian Horse Registry’s application for a Racehorse Identification Supplement asks for, among other things, white markings and other identifying marks or scars, location of cowlicks, photographs of the animal, information on freeze marks and lip tattoos, and parentage qualification through bloodtyping.

        Since the 1970s, the Arabian Horse Registry has required that all breeding stallions have a bloodtype on record. Beginning with 1991 foals, all foals must be bloodtyped and parentage qualified to both sire and dam — which means all broodmares must now have bloodtypes on record before their foals can be registered.

        Only in recent decades has it been possible to verify parentage scientifically. For most of the history of the breed in America, the reliability of pedigrees has rested on the signatures of the owners. With thousands of people breeding, buying, and selling thousands of horses, mistakes can be made.

        An examination of Arabian Stud Book volume V, which covers breeding from the earliest registered American foal (born 1890) up to foals of 1944, turns up several horses with coat color incompatibilities: a grey with no grey parent, or a bay from two chestnut parents. There must be other foals registered with one or both parents recorded incorrectly, but without a coat color incompatibility to flag them.

        Cases of incorrectly recorded parentage might or might not involve a parent from another breed. One example is the 1938 grey gelding Zarab 1525, who has no registered progeny. Well known photographs of both his purported parents exist. They match the colors given in their registration entries; neither was grey. Photographs of Zarab in the Arabian Horse News and in the ranch brochure of his longtime owners show he definitely was grey. Coat color genetics exclude him as the offspring of his purported parents, Rifnas and Hazzadina.

        Does parentage verification by the currently available DNA test have a higher rate of efficacy than parentage verification by bloodtyping? “It’s close to a toss up,” says Dr. Ann Bowling of the lab at the University of California at Davis. “There really is not much difference between efficacy rates. DNA has the advantage that you don’t need blood, or even a live horse if other tissue exists. Bloodtyping’s advantage is that a huge worldwide database is already in place.”

        Could a DNA test be developed to reveal a cross of another breed one or two generations back? Ann Bowling points out that humans and chimpanzees have more than 99% of the same genes. Arabians and Thoroughbreds are far more closely related than humans and chimpanzees: if a horse has 100,000 genes, the Arabian and Thoroughbred may have as few as ten points of variance.

        ”Some of the markers in the Arabian breed do occur infrequently,” she says. “But are they from introgression, or from an under-represented desert source? If you go witch hunting for animals with rare factors, you could end up throwing out more Arabians of acceptable pedigree than you would cross breds.”

        In a recent article, Pepper Chastain of the Department of Animal Science at Texas A&M University makes a similar point. She says “Testing stringent enough to eliminate impure animals would also exclude 1 in 1000 legitimate Arabians from competition.” She also writes, “It is our belief that parentage verification (using DNA typing) at the time of registration is the only real solution for preserving the integrity of the Arabian breed.” (2)

        When asked if the Arabian Horse Registry of America (AHRA) would use DNA testing for parentage verification or as a way to determine “breed purity,” Registrar Ralph Clark responds, “Our only focus is on parentage verification. By multiple generations of parentage verification you don’t have a breed purity issue. The ISAG [International Society of Animal Genetics] agrees this is the only effective way to do this.”

        At the moment, he does not think there is any reason to replace blood typing with DNA testing. “I don’t see a significant advantage when you would have to retest all the horses. If bloodtyping can’t eliminate all but one sire, we will then use DNA — a test with no relationship and a separate efficacy. We feel we can approximate 100% efficacy using DNA as a second alternative.” Other drawbacks he mentioned include that there is yet no protocol for international standardization of DNA test results, and that the results have not been sufficiently tested in court. All that said, he did mention one advantage: “Hair root bulbs for a DNA test are much easier and less expensive to obtain than a blood sample.”

        The American Quarter Horse Association (AQHA) is embracing DNA testing as its preferred method for parentage verification, and is using the lab at Davis. Ralph Clark mentions a few reasons why a shift to DNA testing makes more sense for the AQHA than the AHRA. “They have not had a big bloodtyping program. For the most part, it involved just the major sires. Finally they had to address the question of whether to use bloodtypes or DNA. Converting would be a big problem in a couple of years — the number of animals involved is staggering.”

        The February, 1995 AHRA newsletter summarizes the Arabian Horse Registry’s position: “For the present, the Registry will continue to rely on equine blood typing as the primary means of verification of parentage. The Registry will also continue to monitor advances in equine DNA technology and standardization.”

1. Erika Schiele, The Arab Horse in Europe, p. 244.

2. Pepper Chastain, “Continued DNA Research,” Arabian Finish Line, December 1994, pp. 16-17.